The invention relates to a power tool of the type having a rotation motor drivingly connected to an output shaft via an angle drive.
In particular, the invention concerns a power tool of the above type in which the angle drive comprises a gear casing, a bevelled pinion gear connected to the motor, a bevelled crown wheel connected to the outout shaft and intermeshing with the pinoin gear, and a lubricant dispensing means located in the gear casing and arranged to provide a lubricant to the angle drive.
A problem inherent in many angle type power tools, like rotation grinding or cutting tools, relates to the limited service life of the angle gear. This is mainly due to an insufficient lubrication of the gear teeth of the pinion gear and crown wheel, resulting in a severe frictional wear and heat development in the gearing.
Previously, lubrication of the angle gear has been accomplished simply by filling the gear casing from new with a certain amount of grease and adding some more grease after certain operation intervals. This, however, has turned out to be less satisfactory, because after a relatively short time of tool operation the heavier components of the grease, i.e. the components of higher viscosity, are deposited on the gear casing walls, whereas the lighter components, i.e. the components of lower viscosity, tend to leak out from the gear casing through the output shaft seal means. Such a leakage is larger in pneumatic power tools, because in those tools there is always a certain superatmospheric pressure prevailing in the angle gear casing.
The above problems means that the lubrication intervals have to be rather short not to risk dry operation of the angle gear. It has to be observed, though, that too large an amount of grease in the gear casing will cause a detrimental overheating of the grease as well as the entire angle gear due to internal friction or hysteresis in the grease.
Previous attempts have been made to solve this problem by providing different types of lubricant dispensing means. In U.S. Pat. No. 3,719,254 there is described a power tool angle drive in which a lubricant reservoir is mounted on the output shaft for corotation therewith. This reservoir encloses an absorbent sleeve element which is soaked with a lubricant of a relatively low viscosity and which is arranged to dispense that lubricant by centrifugal action onto the gear teeth at operation of the tool. A drawback with this known device is the limitation in size of the reservoir. Its radial dimension is limited to the space available between the output shaft and the end surface of the pinion gear. The reservoir could of course be extended axially, but that would result in undesireable increased outer dimensions of the angle head. A small size lubricant reservoir results in shorter lubrication intervals.
Another previously suggested solution to the angle drive lubrication problem is described in U.S. Pat. No. 4,403,679. The angle drive disclosed in this patent comprises an absorbent sleeve element immovably mounted in the gear casing surrounding the output shaft. This sleeve, which comprises two portions of different absorption properties, is initially saturated with a lubricant and arranged to meter that lubricant onto the gear teeth of the crown wheel by gravitation. A drawback with this device is that a lubricant with noimparatively low viscosity has to be used. This means in turn that also when the tool is temporarily out of use or stored for a shorter or longer period of time the lubricant is dispensed continuously from the absorbent sleeve. Thereby, the lubricant may be gathered somewhere in the gear casing where it will not be effective to lubricate the gear when the tool is put back in use.
The above identified problem as well as the drawbacks of the previously described devices are overcome by the power tool according to the invention as it is defined in the claims.
A preferred embodiment of the invention is described below with reference to the accompanying drawings.